Georg Heiss

Reef evolution since the Proterozoic is characterized by a long-term increase of reef system modules (microbial, soft/spiculed sponges, calcifying sponges, heterorophic metazoans, photosymbiotic metazoans, coralline algae). Scleractinian reef adaptations since the Late Triassic are denoted by perfecting the photosymbiotic system. Jurassic coral reef ecology still reflects a wider set of growth environments, thus larger niche boundaries relative to today, with different types thriving from brackish, mesotrophic and sediment-loaded, to oligotrophic environments. Tipping point–shifts of modern reefs from healthy to sponge/soft-coral/algae to heterotrophic/microbial reefs appear to reflect in-place 'atavistic' switches to an evolutionary less complex state with a reduced number of modules. The Caribbean Almirante Bay, Panamá, may be a present-day equivalent of adaptation of reefs to increased terrigenous run off and nutrient levels: Isotope and metabolic studies indicate a nutrition with increase of heterotrophy relative to photosymbiotic activity, and changing dominance of hard coral species and species composition structure resemble Jurassic coral reefs of mixotrophic environments characterized by terrigenous runoff. Whether or not these 'atavistic' reef types might firmly establish themselves and might have potential to substitute declining oligotrophic reefs will be strongly governed by the rate and scale of global and local environmental changes. However, owing to their reduced diversity and flat spatial structure these reefs will not be able to substitute all ecosystem services as provided by high-complexity coral reefs. Nevertheless, reef conservation under an anthropocenic view should not only manage and protect oligotrophic 'healthy' reef sites but also those under stress, to allow for 'atavistic' adaptation.

From reefs in the western Indian Ocean at Mayotte (Comoros), Mahe (Seychelles), Ifaty (Madagascar), and La Réunion cores from large coral heads of the genus Porites were sampled. All colonies grow at a water depth between 1m and 9m. Stable isotope records were obtained from skeletal aragonite with a sampling distance of 1mm from the upper part of the cores that comprise between 3 and 6 years of coral growth. All corals showed a clear seasonal signal of d180-values. Correlation with instrumentally recorded sea surface temperatures is generally good for d18O. Sr/Ca-ratios from Réunion Island show an excellent correlation with temperature, which exceeds the accuracy of the d180-thermometer . It is shown that geochemical tracer data from Porites corals provide accurate recordings of SST in the Western Indian Ocean.

This interim report deals with investigations on key factors controlling reef growth by zoophysiologists, ecologists, paleontologists and geologists. The different levels of emphasis are the coral animal and the reef community. The main study area is the Red Sea which reaches over 20°C latitude up to the northernmost margin of the global coral reef belt. Supplementary results on microborer ecology are provided from the Bahamas. The desert enclosed Red Sea, not influenced by land runoff and only minimally by anthropogenic (urban and touristic) nutrient inputs, is predestined for a study on the principal influence of light on calcification within bathymetrical and latitudinal gradients. Hence, on the level of the zooxanthellate scleractinian animal phototrophic and heterotrophic energy supply and its bearing on calcification are being measured in different coral species—in particular inPorites sp., one of the most important reef builders. The growth of 15 zooxanthellate scleractinians in the Gulf of Aqaba correlates with the annual light cycle. This correlation is observable down to 40 m depth. Other growth promoting factors seem to have less influence on coral extension. The availability of organically enriched sediments in shallow water probably yields nutritional value, in particular for filter feeding species, thus restricting their distribution to those areas. Zooxanthellae, when isolated fromMycedium elephantotus, are different in their dependence on depth in maximum rates of photosynthesis and photosynthetic efficiency (-slope). Increasing concentrations of pigments as a function of depth could be determined. Maximum rates of photosynthesis of zooxanthellae in vivo, collected at corresponding depth, have been 4 times higher. Structural and physiological adaptations improving heterotrophic and phototrophic energy intake are highlighted. Porites sp. was the subject of annual growth studies at locations extending from Aqaba in the North over the northern and southern Egyptian coast and islands, Sanganeb Atoll and Wingate reef offshore Sudan to the Gulf of Tadjoura in the Gulf of Aden (Djibouti). Mean growth rates in the shallow water zone increase with decreasing latitude and are highest at the southernmost studied reefs in the Gulf of Tadjoura. However, the observed latitutdinal growth reduction is restricted to the upper ca. 15 m of the water column. The upper limit of growth potential decreases with depth parallel to the decrease of light availability. Highest growth rates are recorded in shallow depth (10–2.9 mm yr−1). This zone reaches at Aqaba (29°30′N) to a depth of ca. 10 m. At the southern Egyptian reefs (24°30′N) this zone extends to ca. 15 m water depth. This effect is probably a result of the stronger reduction of winter light levels and water temperature in the northern regions. Compared to other oceans the decrease of growth with increasing latitude of Red SeaPorites corals is far less, and growth rates at Aqaba are the highest observed at these latttudes. On the level of the community of reef inhabitants four principal topics are addressed: The first one is the dynamics of the proportions of hermatypic and ahermatypic organisms and open space. The occurrence of stony and soft corals and the sharing of empty space in different reef sections at Aqaba and on Sanganeb Atoll were quantified. Soft corals, mainlySinularia- and xeniid species, occupy decreasing shares with depth. Among theXenia species a bathymetrical zonation pattern was detected. The next issue is the growth impeding role of soft corals and gastropod parasites and predators on scleractinians. Experimental and field observations showed xeniid soft corals to be opportunistic i.e. occupying rapidly open space rather than to attacking and outcompeting stony corals. An increasingly specialized behaviour was detected among corallivorous gastropods of the family Coralliophilidae to exploit their coral hosts. Whereas these snails are more or less sessile and depend for a long time on the surrounding host polyps the mobileDrupella cornus (Thaididae) forms feeding aggregations which denude mainly branching corals on shallow reef parts. Furthermore, the role counteracting reef growth of macro- and microbioeroders is investigated.Diadema setosum is a major destructive agent on reefs at Aqaba (not in the central Red Sea). The grazing sea urchins do not only keep potential colonization area free but also erode carbonate material (e. g. 1468 g/m2/year, 10 m depth). Demographic and bathymetric patterns in the sea urchin population are analyzed including their bearing on bioerosion of the reef. Investigations on microboring organisms in carbonate material have started in the Red Sea; initial results, however, are only available from similar studies near Lee Stocking Island, Bahamas. Three major environments have been identified based on the distribution of the different microborers. These are the intertidal environment dominated by boring cyanobacteria., reef sites from 2 to 30 m water depth dominated by a diverse assemblage of boring cyanobacteria and chlorophytes, and the deep reef slope from 100 to 300 m dominated by boring green algae and heterotrophs. The boring chlorophyte genusPhaeophila appears rapidly and dominates at sites from 2 to 30 m, but it leaves vacated borings and is replaced byOstreobium quekettii after 1 year. Different substrate types show very different rates of colonization by microborers. The greatest excavation rates (100 g/m2/3 months) occur in fine-grained limestone, while the slowest rates (0.5 g/m2/3 months) occur in calcite crystals. Molluscan shell material shows intermediate rates of excavation. Light conditions appear very important in determining the growth rate and distribution of different microborers between the sites, however, the interaction of light with other factors, such as substrate, time period of exposure, and water quality conditions may be involved.

The status of coral reefs and coral communities in the Red Sea and Gulf of Aden is generally good, with coral cover averaging 20-50%.  This includes decreases and increase in live coral cover since 2002.  The 1998 bleaching event caused major damage on parts of the southern Red Sea and Gulf of Aden, but caused no damage in the northern Red Sea; in some areas the recovery has been strong, and weak in others.  Recent outbreaks of the crown-of-thorns starfish (COTS) have occurred in Egypt, Saudi Arabia, Djibouti and western Somalia, along with some local bleaching.  Threats to coral reefs differ in the region, but are increasing with the increasing rate of coastal development.  The major local threats include land fills, dredging, sedimentation, sewage discharge and effluents from desalination plants, mostly around towns, cities and tourist development sites.  There is local reef damage around major tourism areas, caused by people and boat anchors, along with other threats.  Fish populations are declining in some areas, because of increased demand for and fishing pressure on food and ornamental species.  Destructive fishing practices such as trawling in fragile habitats is increasing.  There has been an influx of illegal fishing vessels seeking to meet demands of the export market and more affluent and growing populations locally.  The other major threats are from pollution and shipping accidents, and future bleaching.  Monitoring these reefs is becoming increasingly important, as climate change and warmer waters near the limits for coral growth.
Most countries have enacted national legislation for coral reef conservation, and signed multinational agreements with assistance from the Regional Organisation for the Conservation of the Environment of the Red Sea and Gulf of Aden (PERSGA).  However, these laws are either poorly implemented or enforced and often are ignored completely.  The main need is to enforce national and international laws, develop public awareness programs and adopt sustainable management strategies.  This will require long-term strategies for capacity building.  PERSGA developed a Strategic Action Program in 1998 and a Regional Action Plan in 2003 for reef conservation.  The plan aims to reduce impacts with: Integrated Coastal Management; Education and Awareness; Marine Protected Areas; Ecological Sustainable Reef Fisheries; Shipping and Marine Pollution control; and Research, Monitoring and Economic Valuation.  Several major new MPAs are being developed in Djibouti, Eritrea, Saudi Arabia, Sudan, and Yemen.  Management of existing MPAs in a number of countries, including Egypt and Yemen, has improved, with support from the Global Environment Facility and bilateral donors.  A UNDP/GEF Coastal, Marine and Island Biodiversity Project is starting in Eritrea.
100 years ago: Following the opening of the Suez Canal in 1869, the region was a major international shipping route with occasional shipwrecks and related oil spills.  There were invasions of alien species but damage from human activities was minimal.  There were some artisanal fishers but fishing pressure was low and fish stocks were largely unexploited.  The reefs were predominantly healthy.
In 1994: Most reefs were in good condition, with sustainable levels of fishing and low levels of human damage, except near towns, cities and tourist sites.  Some reefs were affected by COTS outbreaks in the 1970s, and bleaching in the early 1990s.
In 2004: Urban growth, coastal land reclamation and fisheries are expanding, and COTS outbreaks are continuing.  Tourism continues to expand in some countries, but not others.  There has been strong recovery of some reefs badly damaged by the 1998 bleaching event, but others have shown no recovery.  There has been some success in establishing MPAs, but there is no effective regional MPA network, and most of the declared MPAs have ineffective management.
Prediction for 2014: Pressure will increase from: major development for mass tourism and industrialisation; over-exploitation and destructive fishing in poorly managed fisheries; COTS outbreaks; and bleaching events.  Over-exploitation of fish throughout much of the region will pose a more serious threat, unless regulations are strengthened and enforcement improved.  Further large-scale bleaching events, like that of 1998, may prove catastrophic to stressed coral reefs in the Gulf of Aden and southern Red Sea.  These impacts will probably lead to decreases in the health and extent of reefs, reduce their renewable goods and services, and lower natural recovery.  However, many reefs in the region will remain healthy, particularly those remote from development or with strong currents or cool upwellings.